Using shells collected from a sediment trap series in the Madeira Basin, we investigate the effects of seasonal variation of temperature, productivity, and optimum growth conditions on calcification ...in three species of planktonic Foraminifera. The series covers an entire seasonal cycle and reflects conditions at the edge of the distribution of the studied species, manifesting more suitable growth conditions during different parts of the year. The seasonal variation in seawater carbonate saturation at the studied site is negligible compared to other oceanic regions, allowing us to assess the effect of parameters other than carbonate saturation. Shell calcification is quantified using weight and size of individual shells. The size-weight scaling within each species is robust against changes in environmental parameters, but differs among species. An analysis of the variation in calcification intensity (size-normalized weight) reveals species-specific response patterns. In Globigerinoides ruber (white) and Globigerinoides elongatus, calcification intensity is correlated with temperature (positive) and productivity (negative), whilst in Globigerina bulloides no environmental forcing is observed. The size-weight scaling, calcification intensity, and response of calcification intensity to environmental change differed between G. ruber (white) and G. elongatus, implying that patterns extracted from pooled analyses of these species may reflect their changing proportions in the samples. Using shell flux as a measure of optimum growth conditions, we observe significant positive correlation with calcification intensity in G. elongatus, but negative correlation in G. bulloides. The lack of a consistent response of calcification intensity to optimum growth conditions is mirrored by the results of shell size analyses. We conclude that calcification intensity in planktonic Foraminifera is affected by factors other than carbonate saturation. These factors include temperature, productivity, and optimum growth conditions, but the strength and sign of the relationships differ among species, potentially complicating interpretations of calcification data from the fossil record.
Unless they adapt, populations facing persistent stress are threatened by extinction. Theoretically, populations facing stress can react by either disruption (increasing trait variation and ...potentially generating new traits) or stabilization (decreasing trait variation). In the short term, stabilization is more economical, because it quickly transfers a large part of the population closer to a new ecological optimum. However, stabilization is deleterious in the face of persistently increasing stress, because it reduces variability and thus decreases the ability to react to further changes. Understanding how natural populations react to intensifying stress reaching terminal levels is key to assessing their resilience to environmental change such as that caused by global warming. Because extinctions are hard to predict, observational data on the adaptation of populations facing extinction are rare. Here, we make use of the glacial salinity rise in the Red Sea as a natural experiment allowing us to analyse the reaction of planktonic Foraminifera to stress escalation in the geological past. We analyse morphological trait state and variation in two species across a salinity rise leading to their local extinction. Trilobatus sacculifer reacted by stabilization in shape and size, detectable several thousand years prior to extinction. Orbulina universa reacted by trait divergence, but each of the two divergent populations remained stable or reacted by further stabilization. These observations indicate that the default reaction of the studied Foraminifera is stabilization, and that stress escalation did not lead to the emergence of adapted forms. An inherent inability to breach the global adaptive threshold would explain why communities of Foraminifera and other marine protists reacted to Quaternary climate change by tracking their zonally shifting environments. It also means that populations of marine plankton species adapted to response by migration will be at risk of extinction when exposed to stress outside of the adaptive range.
We present paleo-water depth reconstructions for the Pefka E section deposited on the island of Rhodes (Greece) during the early Pleistocene. For these reconstructions, a transfer function (TF) using ...modern benthic foraminifera surface samples from the Adriatic and Western Mediterranean Seas has been developed. The TF model gives an overall predictive accuracy of ~50 m over a water depth range of ~1200 m. Two separate TF models for shallower and deeper water depth ranges indicate a good predictive accuracy of 9 m for shallower water depths (0-200 m) but far less accuracy of 130 m for deeper water depths (200-1200 m) due to uneven sampling along the water depth gradient. To test the robustness of the TF, we randomly selected modern samples to develop random TFs, showing that the model is robust for water depths between 20 and 850 m while greater water depths are underestimated. We applied the TF to the Pefka E fossil data set. The goodness-of-fit statistics showed that most fossil samples have a poor to extremely poor fit to water depth. We interpret this as a consequence of a lack of modern analogues for the fossil samples and removed all samples with extremely poor fit. To test the robustness and significance of the reconstructions, we compared them to reconstructions from an alternative TF model based on the modern analogue technique and applied the randomization TF test. We found our estimates to be robust and significant at the 95% confidence level, but we also observed that our estimates are strongly overprinted by orbital, precession-driven changes in paleo-productivity and corrected our estimates by filtering out the precession-related component. We compared our corrected record to reconstructions based on a modified plankton/benthos (P/B) ratio, excluding infaunal species, and to stable oxygen isotope data from the same section, as well as to paleo-water depth estimates for the Lindos Bay Formation of other sediment sections of Rhodes. These comparisons indicate that our orbital-corrected reconstructions are reasonable and reflect major tectonic movements of Rhodes during the early Pleistocene.
Morphologically defined species of marine plankton often harbor a considerable level of cryptic diversity. Since many morphospecies show cosmopolitan distribution, an understanding of biogeographic ...and evolutionary processes at the level of genetic diversity requires global sampling. We use a database of 387 single-specimen sequences of the SSU rDNA of the planktonic foraminifera Globigerinella as a model to assess the biogeographic and phylogenetic distributions of cryptic diversity in marine microplankton on a global scale. Our data confirm the existence of multiple, well isolated genetic lineages. An analysis of their abundance and distribution indicates that our sampling is likely to approximate the actual total diversity. Unexpectedly, we observe an uneven allocation of cryptic diversity among the phylogenetic lineages. We show that this pattern is neither an artifact of sampling intensity nor a function of lineage age. Instead, we argue that it reflects an ongoing speciation process in one of the three major lineages. Surprisingly, four of the six genetic types in the hyperdiverse lineage are biogeographically restricted to the Indopacific. Their mutual co-occurrence and their hierarchical phylogenetic structure provide no evidence for an origin through sudden habitat fragmentation and their limitation to the Indopacific challenges the view of a global gene flow within the warm-water provinces. This phenomenon shows that passive dispersal is not sufficient to describe the distribution of plankton diversity. Rather, these organisms show differentiated distribution patterns shaped by species interactions and reflecting phylogenetic contingency with unique histories of diversification rates.
Chitinous arm hooks (onychites) of belemnoid coleoid cephalopods are widely distributed in Mesozoic sediments. Due to their relative abundance and variable morphology compared with the single, ...bullet-shaped, belemnite rostrum, arm hooks came into the focus of micropaleontologists as a promising index fossil group for the Jurassic–Cretaceous rock record and have been the target of functional, ecological, and phylogenetic interpretations in the past. Based on three well-preserved arm crowns of the Toarcian diplobelid Chondroteuthis wunnenbergi, we analyzed the shape of a total of 87 micro-hooks. The arm crown of Chondroteuthis is unique in having uniserial rather than biserial hooks. The first application of elliptic Fourier shape analysis to the arm weapons of belemnoid coleoids allows for the distinction of four micro-hook morphotypes and the quantification of shape variation within these morphotypes. Based on the best-preserved arm crown, we reconstructed the distribution of morphotypes within the arm crown and along a single arm. Our quantitative data support former observations that smaller hooks were found close to the mouth and at the most distal arm parts, while the largest hooks were found in the central part of the arm crown. Furthermore, we found a distinct arm differentiation, as not every arm was equipped with the same hook morphotype. Here, we report the functional specialization of the belemnoid arm crown for the first time and speculate about the potential function of the four morphotypes based on comparisons with modern cephalopods. Our analyses suggest a highly adapted functional morphology and intra-individual distribution of belemnoid hooks serving distinct purposes mainly during prey capture.
Understanding the biology of reproduction of an organismal lineage is important for retracing key evolutionary processes, yet gaining detailed insights often poses major challenges. Planktonic ...Foraminifera are globally distributed marine microbial eukaryotes and important contributors to the global carbon cycle. They cannot routinely be cultured under laboratory conditions across generations, and thus details of their life cycle remain incomplete. The production of flagellated gametes has long been taken as an indication of exclusively sexual reproduction, but recent research suggests the existence of an additional asexual generation in the life cycle. To gain a better understanding of the reproductive biology of planktonic Foraminifera, we applied a dynamic, individual-based modelling approach with parameters based on laboratory and field observations to test if sexual reproduction is sufficient for maintaining viable populations. We show that temporal synchronization and potentially spatial concentration of gamete release seems inevitable for maintenance of the population under sexual reproduction. We hypothesize that sexual reproduction is likely beneficial during the adaptation to new environments, while population sustenance in stable environments can be ensured through asexual reproduction.
This study reports on reaction processes in a transition
zone from contact to regional metamorphism by using Raman spectroscopy on
carbonaceous matter (RSCM), illite “crystallinity” (Kübler index, ...KI),
chlorite geothermometry, and thermal modeling. The thermal effect due to the
emplacement of the Torres del Paine intrusion (TPI, assembly time of ca. 150 kyr) had different consequences for inorganic and organic compounds of the
host rock. The thermal alteration of the pre-intrusive regional
metamorphosed host rock is documented by elevated RSCM temperatures,
high-temperature chlorite generations, and the appearance of epidote and
retrograde Fe-rich chlorite. Microprobe analysis on chlorite indicates
incomplete re-equilibration as evidenced by various chlorite populations of
individual contact metamorphic samples. This study indicates that the
maturity of organic matter is the most reliable and unequivocal indicator on
timescales of several thousand years to determine the lateral extension of
the TPI contact aureole. Raman geothermometry reveals that the lateral
extension of the contact-influenced zone expands up to a distance of 1.5 km
and, thus, expands to ca. 1.1 km further out than the macroscopically
mappable hornfels contact aureole. The best match between measured (Raman
geothermometry) and calculated (thermal modeling) ΔTmax values
(ΔT=54 ∘C) is achieved with a total intrusion
assembly time of 150 kyr, a magmatic temperature of 800 ∘C, a
two-batch model (batch repose time of 10 kyr) with five pulses per batch,
short heating durations (3 kyr), and long pulse repose times (15 kyr).
ABSTRACT
Spirula spirula (Coleoidea: Decabrachia) is a unique deep-sea squid with an uncertain taxonomic status. Here, we apply geometric morphometric analyses to precisely describe changes in conch ...morphology during the course of ontogeny of 21 specimens collected from 12 localities worldwide. These data were used to explore whether the genus is monospecific or comprises several species. Different 2D and 3D conch parameters are presented based on micro-computed tomography data, combining noninvasive imaging techniques with a range of morphometric analyses. Our data imply that Atlantic and Indo-Pacific specimens form two distinct morphological clusters, potentially representing two pseudocryptic species or two populations undergoing divergence (i.e. in the process of speciation). Given the evolutionary trend from straight to more coiled forms, we suggest that S. spirula represents a neotenous form that migrated from the Indo-Pacific towards the Atlantic via the Agulhas leakage, which has been active since the closure of the Strait of Panama (10–3 Ma).
The state of a population of planktic foraminifers at a
certain time reflects multiple processes in the upper ocean, including
environmental conditions to which the population was exposed during its
...growth, the age of the cohorts, and spatiotemporal patchiness. We carried
out depth-stratified (0–60, 60–100 m) replicated sampling off Puerto
Rico in autumn 2012, revisiting three stations previously sampled in autumn 1994 and spring 1995, in order to analyze seasonal and interannual
variability of planktic foraminifers and the stable isotopic composition of
their tests. The merged dataset from all three sampling campaigns allows us
to assess short- and long-term changes in foraminiferal population dynamics
and the spatial assemblage coherency along the shelf edge. All three
sample series cover more than 2 weeks during either spring (1995) or
autumn (1994, 2012) and include the time of the full moon when reproduction
of some surface-dwelling planktic foraminifers has been postulated to take
place. Our analyses indicate that interannual variability affected the
faunal composition, and both autumn assemblages were characterized by
oligotrophic tropical species, dominated by Trilobatus sacculifer and Globigerinoides ruber (white and pink variety).
However, G. ruber (white) had a higher abundance in 1994 (37 %) than in 2012 (3.5 %), which may be partially due to increasing sea surface temperatures
since the 1990s. Between 60 and 100 m water depth, a different faunal
composition with a specific stable oxygen isotope signature provides
evidence for the presence of the Subtropical Underwater at the sampling
site. Measurements on T. sacculifer sampled in autumn 2012 revealed that test size,
calcification and incidence of sac-like chambers continued to increase after
full moon, and thus no relation to the synodic lunar reproduction cycle was
recognized. During autumn 2012, outer bands of hurricane Sandy passed
the Greater Antilles and likely affected the foraminifers. Lower standing
stocks of living planktic foraminifers and lower stable carbon isotope
values from individuals collected in the mixed layer likely indicate the
response to increased rainfall and turbidity in the wake of the hurricane.
Abstract
Diurnal vertical migration (DVM) is a widespread phenomenon in the upper ocean, but it remains unclear to what degree it also involves passively transported micro- and meso-zooplankton. ...These organisms are difficult to monitor by in situ sensing and observations from discrete samples are often inconclusive. Prime examples of such ambiguity are planktonic foraminifera, where contradictory evidence for DVM continues to cast doubt on the stability of species vertical habitats, which introduces uncertainties in geochemical proxy interpretation. To provide a robust answer, we carried out highly replicated randomized sampling with 41 vertically resolved plankton net hauls taken within 26 hours in a confined area of 400 km2 in the tropical North Atlantic, where DVM in larger plankton occurs. Manual enumeration of planktonic foraminifera cell density consistently reveals the highest total cell concentrations in the surface mixed layer (top 50 m) and analysis of cell density in seven individual species representing different shell sizes, life strategies and presumed depth habitats reveals consistent vertical habitats not changing over the 26 hours sampling period. These observations robustly reject the existence of DVM in planktonic foraminifera in a setting where DVM occurs in other organisms.
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